CuNi40 and CuNi44 wire
An alloy has got its name from lat. — constants — which means «unchanged», «permanent», because its real resistance virtually does not depend on temperature. It is a thermocouple nickel-base of a silver-yellow colour. A presence of cuprum and manganese in alloy composition tinctures such a colour.
Main characteristics of this alloy are:
1. Melting point is 1260 °C;
2. A density of constantan alloy is 8,9 g/cm3;
3. A constant real resistance. A name of alloy has originated from a given characteristics. A coefficient of a thermal expansion is 14•10-6°C-1.
Alloy is widely used in a form of wire, less often in a form of strip or bar (with a diameter 12−100 mm) for producing thermocouples, registries, electric heating elements. Constantan bar is less marketable than a wire, but it is used in a manufacturing of electrical heaters too. Such price is stipulated by the cost of cuprum and nickel that constitute the main components.
It possesses a heat resistance, a plasticity, a constancy of electrical properties. At a temperature of 20 °C a specific electric resistance equals to 0,48 Ohm-mm2/m. After a special process (stabilizing annealing), constantan wire has a coefficient of thermal real resistance that rises to 2×10−6 1/К, in an annealed (soft) comdition constantan eр = 40 — 50%, sр = 400 — 500 MPa and r = 0,45 — 0,48 Ohm-mm2/m; in hard constantan -eр = 2…5%, sр = 650 — 720 MPa and r = 0,46 — 0,52 Ohm-mm2/m.
Such a wire is quite expensive because of nickel presence in its composition. Besides, nickel is prone to damage of a sulfur effect when raising a temperature. The main demerit of a alloy is a huge thermoelectromotive force (40−50 mkV/°С) in a combination with cuprum. Thereby it limits its usage in precise instruments and stable resistors because clue heating of contact elements leads to an appearance of current intensity that impairs indicated values. In this regard, manganin can be used if it is necessary to achieve a high accuracy.
Constantan wire is commonly used in a manufacturing of rheostats, compensating lead wires and heating units. The most popular wire is Ø 0,03−5 mm, and a strip of no more than 0,1 mm. A thermocouple made of constantan wire with cuprum differs with significant thermoelectromotive force and is used at a not very high working temperature (up to 500°С). In such thermocouples, cuprum, chromel or ferrum are positive electrodes; negative are copel and alumel (except of constantan). Thermocouple consists of electric conductor fumes, that are soldered in one end and placed into environment oriented for thermometry («hot junction»). Then, exposed ends are going to be placed into a thermostatic regulator (so-called cold junction). An alloying allows withstanding a short-range effect of a high temperature up to 1300 °C while working in aggressive environment. Constantan wire, less often a strip or a rod are utilized for manufacturing heating controllers and compensating lead wires.
Alloy can be delivered in the following way:
Rod (Ø 12,0 — 100,0 mm);
Strip (0,1−5,0 mm of thickness; 3−600 mm of wideness).
Wire (Ø 0,10 — 11.5 mm);
Percentage composition of constantan CuNi40
|≤ 0.1||≤ 0.5||39 — 41||≤ 0.1||total 0.9||56.1 — 60||1 — 2|
Physical characteristics of constantan CuNi40 at a temperature 20 °C
|Hardness, soft alloy HB 10 -1||480 MPa|
|Hardness, hard alloy HB 10 -1||720 MPa|
|Hot working temperature||1170|
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|Number||Material||Grade||Size (mm)||Rolles stock type||Price|
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